1. Field of the Invention
This invention relates generally to semiconductor processing, and more particularly to devices for generating hot-electron photon emission to methods of using the same.
2. Description of the Related Art
Fault-isolation techniques are critical to the development and manufacture of large scale integrated circuits such as microprocessors. As the numbers of devices per integrated to circuit have continued to climb and the sizes of those devices continued to shrink, methods have been developed to probe the operation of integrated circuits at the device level.
Electron beam micro probing has been used for a number of years as a means of analyzing electrical wave forms generated by the various microscopic circuit structures in an integrated circuit. An electron beam (xe2x80x9ce-beamxe2x80x9d) micro probe is a particularized type of electron microscope that is designed to provide a visual image of the circuit structures on an integrated circuit. E-beams are specifically focused at targeted circuit structures on the integrated circuit and the reaction of the circuit structures to the directed e-beams are sensed by the microscope. Actual electrical test patterns can be used to stimulate the integrated circuit in various ways during the scanning. This is normally accomplished by mounting an integrated circuit on a test board. As with other types of electron microscopy, high vacuum conditions are required for e-beam micro probing.
One method proposed for providing improved imaging over conventional electron beam probing has been coined Picosecond Imaging Circuit Analysis or PICA for short PICA measures time-dependent hot carrier induced light emission from the integrated circuit (IC) both spatially and temporally, thus enabling failure analysis and timing evaluation of a device. Hot electron light emission is generated as a short duration pulse coincident with the normal logic state switching of MOS circuits. This emission can be readily observed and used to directly measure the propagation of high-speed signals through the individual gates. The technique is useful in that non-invasive diagnostics of fully functional MOS devices may be performed.
In one conventional PICA approach, an imaging micro-channel plate photo-multiplier tube (MCP-PMT) is used to detect to the photons. Within the field of view of the objective, the technique allows for parallel acquisition of time resolved emission from many nodes at once. Unfortunately, a typical conventional MCP-PMT detector has low quantum efficiency, especially in the near infrared region. In particular, the detector loses virtually all sensitivity for wavelengths above 900 nm. For acquisition of photon emission from the backside of silicon substrates, this has proved problematic. As a result of the spectral characteristics of hot carrier emission and the optical transmission characteristics of doped silicon, most backside transmitted photons will be in the 900 to 1,500 nm range. Thus, the typical MCP-PMT will detect few of the available photons. This can lead to lengthy acquisition times.
Conventional PICA techniques generally provide rather slow acquisition times. There appear to be three primary parameters that dictate acquisition time for PICA; (1) tester loop time; (2) device operating voltage (xe2x80x9cVDD,xe2x80x9d); and (3) the relative scarcity of PICA photon events. Limitations as to tester loop time are largely functions of data acquisition and computing speed. Device VDD appears to directly affect the frequency of photon events. Manufacturing experience has shown that photon output decreases with decreasing device VDD. The relative scarcity of PICA photon events in general is a function of the somewhat unpredictable quantum mechanical effects of hot electron photon emission in MOS devices.
The present invention is directed to overcoming or reducing the effects of on or more of the foregoing disadvantages.
In accordance with one aspect of the present invention, an apparatus is provided that includes a first circuit device coupled to a first voltage source that is operable to bias the first circuit device to a first voltage, and a second circuit device that has a first input coupled to the first voltage source and a junction defining a first side and a second side. One of the first and second sides is coupled to a second voltage source independent of the first voltage source that is capable of selectively biasing the one of the first and second sides at a second voltage higher than the first voltage. The second device is operable to emit a photon when activated upon application of a bias from the second voltage source.
In accordance with another aspect of the present invention, an apparatus is provided that includes a first circuit device coupled to a first voltage source that is operable to bias the first circuit device to a first voltage. A second circuit device is provided that has a first input coupled to the first voltage source and a junction defining a first side and a second side. One of the first and second sides is coupled to the first voltage source. A voltage step-up device is coupled between the first voltage source and the one of the first and second sides of the junction. The voltage step-up device is operable to selectively bias the one of the first and second sides at a second voltage higher than the first voltage. The second circuit device is operable to emit a photon when activated upon application of a bias from the second voltage source.
In accordance with another aspect of the present invention, an apparatus is provided that includes a CMOS circuit that has an n-channel transistor coupled to a p-channel transistor. The n-channel transistor and the p-channel transistor are coupled to a first voltage source. A transistor is provided that has a first source/drain coupled to an output of the CMOS circuit, a second source/drain coupled to the first voltage source, and a gate coupled to the first voltage source. A diode is coupled between the first voltage source and the gate to enable the transistor to remain in saturation while an output of the CMOS circuit is in a logic high state, such that the transistor is operable to emit hot-electron induced photons while the output of the CMOS circuit is in the logic high state.
In accordance with another aspect of the present invention, a method of examining a circuit device is provided that includes causing a first circuit device with an operating voltage to switch from a first logic state to a second logic state in response to a control signal. The first circuit has a switching speed. A second circuit device is caused to conduct current in response to the control signal. The the current flow is maintained through the second circuit second circuit device for longer than the switching speed. Photons emitted from the second circuit device are observed.
In accordance with another aspect of the present invention, an apparatus is provided that includes a plurality of circuit devices that have respective outputs. A multiplexer coupled to the respective outputs that is operable to provide a multiplexed output. A second circuit device is provided that has a first input coupled to the multiplexed output, and a junction defining a first side and a second side. One of the first and second sides is coupled to a second voltage source capable of selectively biasing the one of the first and second sides at a second voltage higher than the first voltage. The second device is operable to emit a photon when activated upon application of a bias from the second voltage source.